New York: French drug-maker Sanofi-aventis on Monday said it has extended the validity of its $18.5 billion offer for US biotechnology firm Genzyme Corporation till 21 January.

Sanofi-aventis’ offer of $69 per Genzyme share was scheduled to expire on 10 December. About 2,211,989 shares, or 0.9% of the outstanding shares of the company, had been tendered by the midnight deadline, Sanofi-aventis said in a statement.

“In order to provide additional time to allow holders of Genzyme common stock to tender their shares, the tender is now scheduled to expire at 11.59 pm, New York City time, on 21 January, 2011, unless it is further extended," Sanofi- aventis said.

The transaction is valued at approximately $18.5 billion. The offer represents a premium of 38% over Genzyme’s share price of $49.86 on 1 July.

The French firm had gone directly to Genzyme’s shareholders on 4 October, after company CEO Henri Termeer said the bid “undervalues" the company. Sanofi-aventis’ offer to buy Genzyme was made public in August, when it had also hinted at the possibility of an unfriendly takeover.

Sanofi-aventis said it had tried to engage in constructive discussions with Genzyme, “but the latter’s continued refusal to do so led to the hostile offer."

In September, Sanofi CEO Christopher Viehbacher had told Termeer that the company would be willing to pay between $69 and $80 a share for Genzyme.

Sanofi-aventis has a significant presence in India and employs over 1,800 people in the country.

Last year, Sanofi-aventis had sought to acquire an 80 per cent stake in Hyderbad-based Shantha Biotechnics for $784 million.